Nematic structures in randomly interconnected porous hosts

Deuteron NMR measurements were performed on the octyl-cyanobiphenyl (8CB) L iquid crystal confined to the randomly interconnected and large cavities of cellulose acetate Millipore filters and to the small pores of silica aerog el. These studies were performed as a function of sample orientation in the field, and by changing the confining size. In almost all cases, 8CB was co nfined to sizes smaller than the micron size magnetic coherence length, thu s the observed line-shapes reflect the director pattern, (n) over cap((r) o ver right arrow), and the orientational order, Q, as dictated by the porous host. The isotropic nature of aerogel yields DNMR spectral patterns consis tent with powder-lineshapes. These patterns indicate a randomized (n) over cap((r) over right arrow), characterized by a single e. No angular dependen ce is found and nematic domains of finite dimension most likely exceeding t he confining size are formed. In contrast, the Millipore anisotropy and lar ger confining sizes yield DNMR patterns dependent on the sample orientation in the field and show a competition between surface-induced and field indu ced molecular alignment.